Hello fellow woodworkers,
I’m planning to build two “built-in” bookcases for my living room. The units will be painted to match the walls and trim. I’m thinking of building the units out of lightweight MDF. Now, I’ve never used this stuff before. I interested to know how the lightweight MDF holds paint and which fasteners would be best (screws, nails, staples)?
Thanks for the help.
Jay M
Edited 9/26/2002 11:20:55 AM ET by JAYMAUKSCH
Replies
is there such a thing as lightweight mdf?
My back would love to find this stuff.
I've built "tons" of stuff out of mdf, and i use glue and drywall screws, counter sunk. because it can split.
It takes paint great, but the edges will need lot's of sanding, sawing usually leaves the sides pretty rough. I usually sand after each coat of paint, except that last one.
Use the same fasteners you use on regular MDF. Have you worked wirh MDF before? Drywall srews are ok and there are better screws you can use. Check McFeely's. Confirmat screws are nice but over kill.
Rick
Edited 9/26/2002 12:23:47 PM ET by rsl
Edited 9/26/2002 12:24:20 PM ET by rsl
I've tried lightweight MDF, and was unimpressed. It has some the drawbacks of standard MDF: it bends more than plywood; it doesn't hold screws as well; and the "grain" raises a great deal under water-borne finishes. In addition, in my area it costs much more than standard MDF, and almost as much as plywood. For the small price difference, I went back to paint-grade cabinet plywood.
use a shellac based primer for MDF. as for the shelves, MDF needs bracing to support the loads. Lightweight MDF is a myth.... BTW use only carbide cutters, and MDF can be hard on the carbide.
No, lightweight MDF is not a myth. A 3/4" sheet of standard MDF weighs about 90 pounds. A 3/4" sheet of lightweight MDF weighs about 70 pounds.
Edited 9/26/2002 3:45:05 PM ET by JAMIE_BUXTON
is say lighter weight, not lightweight..... 2.8lbs vs 2.1 lbs a sq foot to me isnt that much a back saver :)
Yeah, our bodies are all calibrated differently. For me, a full sheet of 3/4" standard MDF is pretty darn difficult to lift. "Lightweight" MDF, which weighs 20 pounds less, is much better. However, real plywood weighs about the same as "lightweight" MDF, and beats it all hollow in almost every other way.
>> ... MDF needs bracing to support the loads.
Maybe. Maybe not. It depends on the span.
Gentlemen (and ladies?), I have several bookcases and cabinets constructed out of some melamine-coated, 3/4' stuff like this (or maybe it's particleboard--whatever it is, it weighs about a jillion pounds), and although the shelves span only 30," the bottom shelves, especially, are sagging noticeably under the weight of my taunton sewing subscriptions (I got here via the sewing forum).
Is there some way for a woman to shore up or reinforce the shelves of such cabinets or cases? If they weren't already assembled, I could see maybe some possibilities, but these suckers are glued and doweled together, and a couple of them have doors that need to close.
If you can give up 3/4" of vertical space between shelves, the simplest fix would probably be to glue another layer of 3/4" melamine to the top or bottom of the shelves. Doubling the thickness of the shelves should reduce the deflection by a factor of 8.
If you can put blocks or bricks or old paperback books or something under the bottom shelf, then you could put a piece of plywood or shelving vertically under each subsequent shelf. If you cut them to just the right length you wouldn't need any fasteners, but running a screw or two into the top of each one might be easier.
Other possibilities include cleats on the back, hardwood stiffeners let into the front edges, angle iron screwed and glued to the bottom of the shelves, etc.
Thank you, Uncle Dunc. That gives me some very workable solutions to try, and ones I would not have thought of. I do appreciate your help, especially the notion of changing the loading capacity of the shelving via thickness. I can indeed sacrifice 3/4."
FHB had a thread on treating cut edges of mdf. Paint the edges with glue (I belive a 30% mix of glue and water) and then use a shellac primer.
Jay, check out my prior post on screws for MDF:
http://forums.taunton.com/tp-knots/messages/?msg=7978.4
In addition to everything previous: Hi-lo screws are typically recommended. Spackling can cure some of the downsides of edge painting. MDO ply would likely do the same thing with a better paint base and more structural integrity, and in a bookcase, that seems prudent.
I'm going to do the same thing, but for a home office. I was planning to use birch plywood even though, like your project, it will be painted the same color as the room and trim. I don't like MDF for lots of reasons: the gunk it produces when sawing and grooving it.. it's inability to hold drywall screws.. it's lack of structural strength.. and the fact that it just plain ain't WOOD. I might use MDO if I could find it but I can't. I've had two wood supply guys look at me funny when I asked for it. When I said "medium density overlay" they said, "Oh, we don't carry that."
Bill
Where I live they're calling the stuff LDF now, and I like it for certain things, since it machines beautifully - you can use it for drawer fronts and even baseboards, but it's not as durable as MDF, and it has zero structural integrity. I think you should use birch plywood - you'll get a much nicer product in the long run and the extra cost of the materials is insignificant compared with the amount of time you'll spend on the project.
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